The discomfort associated with the injection of anesthetics results from the pressure of the incoming fluid. To minimize the discomfort, the anesthetic can be injected very slowly at first to numb the nerves and tissue at the point of the injection. The fluids can then be introduced at a higher rate without discomfort.
Known devices include motor driven syringes and microprocessor-controlled pumps. For example, U.S. Pat. No. 5,807,334 employs a motor built into the syringe to depress the plunger of a syringe cartridge. Multiple gears provide slow flow rates and faster flow rates. A number of devices employ a microprocessor-controlled pump to control anesthetic flow rates. In one example of a microprocessor-controlled pump, the pump is in a unit distant from the hand held needle-bearing device. Tubing is then necessary to transmit the fluid from the pump to the needle. In another example, U.S. Patent App. Pub. No. 2001/0007327 Al employs repeated strokes on an altered syringe cartridge to meter the flow of anesthetic.